Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $32.57   6.806%   $34.7867   $34.79   $34.80   $34.80  
  Purchase #2 $248.35   4.581%   $259.7269   $259.73   $259.75   $259.70  
  Purchase #3 $46.86   9.285%   $51.211   $51.21   $51.20   $51.20  
  Purchase #4 $111.62   9.465%   $122.1848   $122.18   $122.20   $122.20  
  Purchase #5 $170.91   11.760%   $191.009   $191.01   $191.00   $191.00  
  Purchase #6 $180.46   13.830%   $205.4176   $205.42   $205.40   $205.40  
  Purchase #7 $94.81   13.268%   $107.3894   $107.39   $107.40   $107.40  
  7 purchase totals = $885.58       $971.7254   $971.73   $971.75   $971.70